1. Field of the Invention
The present invention relates to a fluid compressor for compressing a refrigerant gas, designed for use in a refrigerating apparatus, for example.
2. Description of the Related Art
The applicants hereof have proposed a fluid compressor which comprises a sealed case, a cylinder located in the case, and a piston inserted in the cylinder. The piston is positioned eccentric to the cylinder and set in rolling contact with the inner circumferential surface of the cylinder. It has a helical groove cut in its circumferential surface and having a pitch gradually decreasing toward one end of the piston. A helical blade is loosely fitted in the helical groove. The blade partitions the annular space between the piston and the cylinder, defining a plurality of helical compression chambers. The chamber has a cross section gradually decreasing toward one end of the piston.
The fluid compressor has a mechanism. When the cylinder is rotated, the mechanism transmits a rotational force to the piston. The piston is thereby rotated, remaining eccentric to the cylinder. As the cylinder and the piston are rotated, a portion of each turn of the blade protrudes from the groove, while the diametrically opposite portion of the turn retracts into the groove.
As the cylinder and the piston are thus rotated, a medium to be compressed, e.g., a refrigerant gas, is drawn into the cylinder from a refrigerating circuit. The refrigerant gas flows to the gas-inlet end of the cylinder. In the cylinder, the gas and is gradually compressed in the cylinder until its pressure reaches a predetermined value. The gas is discharged from the compression chamber and guided into the refrigerating circuit.
Various types of mechanisms are known which can transmit a rotational force of the cylinder to the piston. The most popular of these is a so-called Oldam mechanism which comprises an oldham ring receiver to be coupled to the cylinder, a key section to be connected to the piston, and an oldham ring held by the oldham ring receiver and the key section and able to slide.
An oldham ring is a mechanical element which revolves around an object to which it transmits a force, while controlling the rotation of that object. If incorporated in a compressor of the above-mentioned type, the oldham ring needs to rotate as the cylinder and the piston are rotated. Since the oldham ring must rotate while revolving around the piston, it must be made of a suitable material. If made of a material having an excessive specific gravity (i.e., density), the oldham ring is likely to generate vibration, impact and noise.
The oldham ring may not be resistant to impact and may generate much vibration and noise if it has not been machined with precision in both shape and size. Furthermore, if not machined with precision, the oldham ring may wear to jeopardize the reliability of the fluid compressor in which it is used.
Jpn. Pat. Appln. KOKAI Publication No. 5-44401 suggest that an oldham ring for use in a scroll-type compressor be made of ceramics so as to be sufficiently resistant to impact, to generate but little vibration and noise, and to have sufficiently wear resistance. A oldham ring designed for use in a scroll-type compressor need not rotate around its axis; it needs only to revolve around an object. Hence, it is only required that the Oldam ring be sufficiently resistant to wear.